The invention relates to the field of intravascular delivery systems, and more particularly to balloon catheters for stent delivery in the intracranial vasculature, referred to herein as neurovasculature.
In neurovascular angioplasty procedures a guiding catheter is advanced until the distal tip of the guiding catheter is just proximal to the origin of the intracranial arteries that lead to the target vascular site. A guidewire, positioned within an inner lumen of a dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient""s intracranial vasculature until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter, having an inflatable balloon on the distal portion thereof, is advanced into the patient""s intracranial vasculature over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid saline or radiopaque contrast one or more times to a predetermined size at relatively high pressures (e.g. at least about 4-6 atmospheres) so that the lesion is dilated to restore vessel patency. However, damage to the vessel wall at and around the lesion can result from the expansion of the balloon against the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated vessel and the dilatation catheter can be removed therefrom.
In such neurological angioplasty procedures, there may be restenosis of the lesion due to acute or sub-acute (chronic) complications, such as vessel recoil, lesion dissection, intimal hyperplasia, or other factors. The resulting restenosis may in turn necessitate either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. In similar coronary angioplasty, the restenosis rate is reduced and the dilated area is strengthened by implanting an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. However, currently, this treatment modality is not available in neurovascular applications due primarily due to the inability to access the distal, highly tortuous anatomy of the neurovascular system with conventional stent delivery systems. Further details of stents and stent delivery systems for PTCA procedures can be found in U.S. Pat. No. 5,507,768 (Lau et al.), U.S. Pat. No. 5,458,615 (Klemm et al.), and U.S. Pat. No. 5,514,154 (Lau et al.), which are incorporated herein by reference in their entireties. Commonly used coronary stent delivery systems are too inflexible to track through the neuro anatomy. Furthermore, they tend to kink when bent into tight radius curves.
Therefore, what has been needed is a catheter and stent delivery system suitable for use in neurovascular applications. The present invention satisfies these and other needs.
The present invention is directed to a balloon catheter, such as a dilatation catheter and a stent delivery catheter with improved stiffness transition and specifically with no sudden changes in stiffness along the catheter length. In the balloon catheters of the invention alone or mounted with a stent, whether used for peripheral, coronary, or neurovascular applications, is important to reduce the significant bending stiffness changes (herein referred to as bending stiffness discontinuity) present along the length of the catheter. It should also be appreciated that although in describing features of the present invention, the features are directed primarily to a neurovascular stent delivery system, the invention is also applicable to coronary and peripheral stent delivery systems, as well as dilatation catheters for peripheral, neurological, coronary, and similar applications.
Having smooth transitions from one region to another along the length of the catheter, in particular, when a stent is located on the catheter, is of particular importance in neurovascular applications. The major design challenge for a Neurovascular Stent Delivery System (NSDS), in particular, has been in improving the ability to access the distal, highly tortuous anatomy of the neurovascular system. In order to meet this challenge, the present invention provides for a catheter and stent delivery system optimized for flexibility and kink-resistance. Improved flexibility allows the device to turn tight corners along the vasculature without applying large forces against the wall of the vessels, thus minimizing the surface friction between the catheter and the vessel. This allows more distal access, particularly in tortuous neurovascular anatomy.
The optimization of flexibility for the neurovascular stent delivery system may aggravate the kinking dynamic, as for example, bending stiffness discontinuities can be more pronounced as some softer catheter members are more likely to kink than stiffer members. Kinking of the catheter is also a common constraint to distal access. The kink creates a hinge point in the catheter so that the catheter can no longer navigate tight radius turns in the vasculature. Kinks often occur at the interface of two regions along the device having substantially different bending stiffness (i.e., have a discontinuity in the bending stiffness). Examples of such interfaces, include, but are not limited to: the proximal and distal ends of a stent disposed on a catheter, and areas adjacent the balloon seals and marker bands.
The stent delivery system of the present invention, in particular as adapted for neurovascular applications, has been optimized for flexibility and kink resistance. The kink resistance has been achieved by minimizing the differential in bending stiffness at the troublesome regions. The present invention includes various embodiments for minimizing the bending stiffness differential as well as increasing the overall flexibility of the catheter, including but not limited to one or more of the following: (1) the lengthening and softening of the catheter tip and the distal balloon seal while maintaining a low profile, (2) crimping the ends of the stent onto the marker bands, (3) locating stiffening sleeves on the inner member on or near the ends of the stent, (4) using a variable stiffness inner member, and (5) providing variable stiffness sheath on the catheter particularly over the stent; in order to reduce the stiffness differential among adjacent portions along the catheter.
In the practice of the present invention, the areas of low bending stiffness located immediately before or after an area of higher bending stiffness may be xe2x80x9cbuilt upxe2x80x9d in stiffness to gradually transition the stiffness of that portion to an adjacent portion of higher value, thus providing a relatively smooth transition from one region to another.
In other words, the present catheter has more than one portion with different stiffness values, each portion comprising of components that gradually transition the stiffness of that portion to an adjacent portion, thus reducing the differential in bending stiffness in moving from one region to another, when the catheter is used alone or in combination with a stent in a stent delivery system.
The stent delivery system of the present invention includes a catheter having an elongated shaft with proximal and distal ends and an inner lumen extending therein. The system further includes an enlargable member mounted on a distal shaft section proximal to the distal end which is configured for supporting a deployable prosthetic device on a receiving portion thereon. The enlargable member has an interior in fluid communication with the inner lumen. Furthermore, a tubular member extends through the interior of the enlargable member.
In one embodiment, the stent delivery system further includes proximal and distal radiopaque markers disposed on a portion of the tubular member extending within the interior of the enlargable member. Preferably, a portion of each marker is within and a portion is outside the receiving portion of the enlargable member. Optionally, the catheter system may further include at least one jacket disposed on a portion of the tubular member extending within the interior of the enlargable member. The jacket overlays, at least in part, at least one of the proximal and distal markers. The jacket, preferably, extends, at least in part, outside the receiving portion of the enlargable member. The jacket may include an outer and an inner layer. A portion of the inner layer is adjacent the tubular member extending through the interior of the enlargable member. The system may further include at least one outer jacket formed of a material relatively stiffer than the jacket material. The outer jacket butts up to at least one of the proximal and distal markers. The at least one outer jacket may be, at least partially, overlaid with the jacket.
Alternatively the stent delivery system further includes more than one portion with different stiffness values. Each portion comprises of components that gradually transition the stiffness of that portion to an adjacent portion. Preferably., the stiffness ratio between any two adjacent portions is at least 0.3, more preferably from about 0.3 to about 0.7, and most preferably, at least 0.7. Alternatively, the system further include an outer tubular member and an inner tubular member. The outer tubular member may include more than one section, the sections having a decrease in stiffness in the distal direction. The inner member may include more than one section, the sections having a decrease in stiffness in the distal direction. Alternatively, the stiffness of a portion of the inner tubular member may be built up to more smoothly match,the stiffness of an adjacent portion of higher stiffness. Alternatively, the system may further include proximal and distal radiopaque markers disposed on a portion of the tubular member extending within the interior of the enlargable member. Alternatively, the at least one portion of the tubular member extending within the interior of the enlargable member includes a tubular member with an imbedded coil for providing a gradual transition in stiffness of that portion to the enlargable member receiving portion upon receiving the deployable member thereon. Alternatively, the system may further include a retractable sheath disposed over at least a portion of the catheter shaft for covering the deployable member once the deployable member is mounted on the catheter. The sheath, preferably, has a variable stiffness to minimize kinking of the catheter near or at proximal and distal ends of the deployable member.
In another embodiment, the stent delivery system further includes at least one radiopaque segment having proximal and distal ends. The at least one radiopaque segment is disposed, at least in part, within the enlargable member. The catheter shaft has a sufficiently gradual change in stiffness from a point proximal to the proximal end of the radiopaque segment to at least the proximal end of the radiopaque segment to minimize kinking of the catheter upon application of force during a medical procedure. Additionally, the enlargable member includes a deployable member receiving portion having proximal and distal receiving ends with the at least one radiopaque segment located longitudinally within and outside the deployable receiving portion. Alternatively, the radiopaque segment has a conical shape with a conicity away from the receiving portion. Alternatively, the radiopaque segment is integral with the tubular member extending through the enlargable member.
Alternatively, the stent delivery system further includes an outer tubular member and an inner tubular member with a distal inner member having a portion extending through the enlargable member. The extending portion of the distal inner member includes at least one tubular sleeve disposed about and attached to the distal inner member. The at least one tubular sleeve has sufficient stiffness to provide a relatively smooth stiffness transition from a point along the catheter shaft proximal to a proximal edge of the at least one tubular sleeve to a point along the catheter shaft distal to a distal edge of the at least one tubular sleeve. Additionally, the proximal tubular sleeve is extended into a distal end of the outer tubular member forming a proximal overlap region to minimize proximal transition kinking. Optionally, a portion of the distal end of the outer tubular member is extended into the proximal section of the enlargable member and the proximal overlap is located within the extended portion.
In another embodiment, the stent delivery system further includes an outer tubular member having a distal edge and an inner tubular member. The distal edge of the outer tubular member extends distally to a point being at the same transverse location or proximal to a proximal end of the receiving portion. Optionally, the distal edge of the outer tubular member may extend distal to the proximal end of the receiving portion.
In another embodiment, the stent delivery system the enlargable member forms proximal and distal fluid-tight seals with the catheter shaft at the enlargable member proximal end and distal ends, respectively. The distal seal of the enlargable member may have perforations or grooves thereon to provide a gradual stiffness reduction in the distal direction.
In another embodiment, the stent delivery system further includes a catheter tip at the shaft distal end and includes an atraumatic distal tip having a distal end. The tubular member extending through the enlargable member has a distal end which is butt-joined to a proximal end of the atraumatic distal tip. An outer layer member may be butt-jointed or lap-jointed to the distal end of the enlargable member at a point proximal to the tubular member distal end. The outer layer extends distally to a point proximal to the distal end of the atraumatic distal tip.
The balloon catheter of the present invention includes a catheter having an elongated shaft with proximal and distal ends and an inner lumen extending therein. The system further includes an enlargable member mounted on a distal shaft section proximal to the distal end. The enlargable member has an interior in fluid communication with the inner lumen. Furthermore, a tubular member extends through the interior of the enlargable member.
In one embodiment, the balloon catheter further includes proximal and distal radiopaque markers disposed on a portion of the tubular member extending within the interior of the enlargable member. Optionally, the balloon catheter may further include at least one jacket disposed on a portion of the tubular member extending within the interior of the enlargable member. The at least one jacket overlays, at least in part, at least one of the proximal and distal markers.
Alternatively the balloon catheter further includes more than one portion with different stiffness values. Each portion comprises of components that gradually transition the stiffness of that portion to an adjacent portion. Preferably, the stiffness ratio between any two adjacent portions is at least 0.3, more preferably from about 0.3 to about 0.7, and most preferably, at least 0.7. Alternatively, the balloon catheter further include an outer tubular member and an inner tubular member. The outer tubular member may include more than one section, the sections having a decrease in stiffness in the distal direction. The inner member may include more than one section, the sections having a decrease in stiffness in the distal direction. Alternatively, the stiffness of portion of the inner tubular member may be built up to more smoothly match the stiffness of an adjacent portion being of higher stiffness. Alternatively, the balloon catheter may further include proximal and distal radiopaque markers disposed on a portion of the tubular member extending within the interior of the enlargable member. Alternatively, the at least one portion of the tubular member extending within the interior of the enlargable member includes a tubular member with an imbedded coil for providing a gradual transition in stiffness of that portion to an adjacent portion of higher stiffness. Alternatively, the balloon catheter may further include a sheath disposed over at least a portion of the enlargable member. The sheath, preferably, has a variable stiffness to minimize kinking of the catheter near or at the enlargable member.
In another embodiment, the balloon catheter further includes at least one radiopaque segment having proximal and distal ends. The at least one radiopaque segment is disposed, at least in part, within the enlargable member. The catheter shaft has a sufficiently gradual change in stiffness from a point proximal to the proximal end of the radiopaque segment to at least the proximal end of the radiopaque segment to minimize kinking of the catheter upon application of force during a medical procedure. Additionally, at least one radiopaque segment may be located longitudinally within the interior of the enlargable member. Alternatively, the radiopaque segment has a conical shape with a conicity away from the intermediate section of the enlargable member. Alternatively, the radiopaque segment is integral with the tubular member extending through the enlargable member.
Alternatively, the balloon catheter further includes an outer tubular member and an inner tubular member with a distal inner member having a portion extending through the enlargable member. The extending portion of the distal inner member includes at least one tubular sleeve disposed about and attached to the distal inner member. The at least one tubular sleeve has sufficient stiffness to provide a relatively smooth stiffness transition from a point along the catheter shaft proximal to a proximal edge of the at least one tubular sleeve to a point along the catheter shaft distal to a distal edge of the at least one tubular sleeve. Additionally, the proximal tubular sleeve is extended into a distal end of the outer tubular member forming a proximal overlap region to minimize proximal transition kinking. Optionally, a portion of the distal end of the outer tubular member is extended into the proximal section of the enlargable member and the proximal overlap is located within the extended portion.
In another embodiment, the balloon includes proximal and distal sections with an intermediate section therebetween. The balloon catheter further includes an outer tubular member having a distal edge and an inner tubular member. The distal edge of the outer tubular member extends distally within the intermediate portion of the enlargable member. Optionally, the distal edge of the outer tubular member may extend distal to a proximal end of the intermediate section.
In another embodiment, the enlargable member of the balloon catheter forms proximal and distal fluid-tight seals with the catheter shaft at the enlargable member proximal end and distal ends, respectively. The distal seal of the enlargable member may have perforations or grooves thereon to provide a gradual stiffness reduction in the distal direction.
In another embodiment, the balloon catheter further includes a catheter tip at the shaft distal end and includes an atraumatic distal tip having a distal end. The tubular member extending through the enlargable member has a distal end which is butt-joined to a proximal end of the atraumatic distal tip. An outer layer member may be butt-joined to the distal end of the enlargable member at a point proximal to the tubular member distal end. The outer layer extends distally to a point proximal to the distal end of the atraumatic distal tip.